Oxide semiconductor transistor and manufacturing method thereof

ABSTRACT

An oxide semiconductor transistor includes an oxide semiconductor channel layer, a metal gate, a gate insulation layer, an internal electrode, and a ferroelectric material layer. The metal gate is disposed on the oxide semiconductor channel layer. The gate insulation layer is disposed between the metal gate and the oxide semiconductor channel layer. The internal electrode is disposed between the gate insulation layer and the metal gate. The ferroelectric material layer is disposed between the internal electrode and the metal gate. The ferroelectric material layer in the oxide semiconductor transistor of the present invention is used to enhance the electrical characteristics of the oxide semiconductor transistor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transistor and a manufacturing method thereof, and more particularly, to an oxide semiconductor transistor including a ferroelectric material layer and a method of forming the same.

2. Description of the Prior Art

Oxide semiconductor materials, such as indium gallium zinc oxide (IGZO), have been applied in thin film transistors (TFTs) of display devices and field effect transistors (FETs) used in integrated circuits because of properties such as high mobility and low leakage current. However, although the leakage current of the transistor including the oxide semiconductor layer is relatively low, the application field of the present oxide semiconductor transistor is still limited because the threshold voltage (Vt) of the oxide semiconductor transistor is still too high and the on-current (I_(on)) of the oxide semiconductor transistor is not high enough for some application such as low power devices. For example, the gate insulation layer in the oxide semiconductor transistor has to be thick enough (thicker than 100 angstroms for example) for keeping low leakage current, and the on-current is limited by the thicker gate insulation layer. The gate voltage (Vg) and the drain voltage (Vd) are also too high because of the relatively higher threshold voltage of the oxide semiconductor transistor, and the oxide semiconductor transistor cannot be applied in the low power devices accordingly. Therefore, it is an important subject for the related industries to improve the electrical performances of the oxide semiconductor transistor without deteriorating the original property of low leakage current.

SUMMARY OF THE INVENTION

An oxide semiconductor transistor and a manufacturing method thereof are provided by the present invention. A ferroelectric material layer is disposed between a metal gate and an internal electrode for forming a negative capacitance effect. The on-current of the oxide semiconductor transistor may be enhanced, and the oxide semiconductor transistor may be applied in low power operation accordingly.

According to one embodiment of the present invention, an oxide semiconductor transistor is provided. The oxide semiconductor transistor includes an oxide semiconductor channel layer, a metal gate, a gate insulation layer, an internal electrode, and a ferroelectric material layer. The metal gate is disposed on the oxide semiconductor channel layer. The gate insulation layer is disposed between the metal gate and the oxide semiconductor channel layer. The internal electrode is disposed between the gate insulation layer and the metal gate. The ferroelectric material layer is disposed between the internal electrode and the metal gate.

According to one embodiment of the present invention, a manufacturing method of an oxide semiconductor transistor is provided. The manufacturing method includes the following steps. A gate insulation layer is formed on an oxide semiconductor channel layer. An internal electrode is formed on the gate insulation layer. A ferroelectric material layer is formed on the internal electrode. A metal gate is formed on the ferroelectric material layer. At least a part of the ferroelectric material layer is disposed between the metal gate and the internal electrode.

In the oxide semiconductor transistor of the present invention, the ferroelectric material layer and the internal electrode disposed between the metal gate and the gate insulation layer may be used to form a negative capacitance effect, and the negative capacitance effect may be used to amplify the gate voltage. The purposes of increasing the on-current and lowering the sub-threshold swing (SS) may be achieved accordingly. In addition, the gate insulation layer may become thinner without influencing the low leakage current performance because of the ferroelectric material layer, the oxide semiconductor transistor may be used in low power operations, and the application field of the oxide semiconductor transistor may be expanded accordingly.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing illustrating an oxide semiconductor transistor according to a first embodiment of the present invention.

FIG. 2 is a schematic drawing illustrating an oxide semiconductor transistor according to a second embodiment of the present invention.

FIGS. 3-5 are schematic drawings illustrating a manufacturing method of the oxide semiconductor transistor according to the second embodiment of the present invention, wherein

FIG. 4 is a schematic drawing in a step subsequent to FIG. 3, and

FIG. 5 is a schematic drawing in a step subsequent to FIG. 4.

FIG. 6 is a schematic drawing illustrating an oxide semiconductor transistor according to a third embodiment of the present invention.

FIG. 7 is a schematic drawing illustrating an oxide semiconductor transistor according to a fourth embodiment of the present invention.

FIG. 8 is a schematic drawing illustrating a manufacturing method of the oxide semiconductor transistor according to the fourth embodiment of the present invention.

FIG. 9 is a schematic drawing illustrating an oxide semiconductor transistor according to a fifth embodiment of the present invention.

FIG. 10 is a schematic drawing illustrating an oxide semiconductor transistor according to a sixth embodiment of the present invention.

FIG. 11 is a schematic drawing illustrating a manufacturing method of the oxide semiconductor transistor according to the sixth embodiment of the present invention.

FIG. 12 is a schematic drawing illustrating an oxide semiconductor transistor according to a seventh embodiment of the present invention.

FIG. 13 is a schematic drawing illustrating an oxide semiconductor transistor according to an eighth embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1. FIG. 1 is a schematic drawing illustrating an oxide semiconductor transistor according to a first embodiment of the present invention. As shown in FIG. 1, an oxide semiconductor transistor 100 is provided in this embodiment. The oxide semiconductor transistor 100 includes an oxide semiconductor channel layer 10, a metal gate 29, a gate insulation layer 22, an internal electrode 23, and a ferroelectric material layer 24. The metal gate 29 is disposed on the oxide semiconductor channel layer 10. The gate insulation layer 22 is disposed between the metal gate 29 and the oxide semiconductor channel layer 10. The internal electrode 23 is disposed between the gate insulation layer 22 and the metal gate 29. The ferroelectric material layer 24 is disposed between the internal electrode 23 and the metal gate 29. In other words, the gate insulation layer 22, the internal electrode 23, the ferroelectric material layer 24, and the metal gate 29 are stacked sequentially on the oxide semiconductor channel layer 10 in a vertical direction D1. Because of the material properties of the ferroelectric material layer 24, a negative capacitance effect may be formed by the ferroelectric material layer 24 disposed between the metal gate 29 and the internal electrode 23. The negative capacitance effect may be used to amplify the gate voltage applied to the metal gate 29, and the on-current (I_(on)) of the oxide semiconductor transistor 100 may be enhanced accordingly. Additionally, the negative capacitance effect may also be used to decrease the sub-threshold swing (SS), and the oxide semiconductor transistor 100 may be applied in low power operation devices accordingly. For example, in a condition without the ferroelectric material layer 24, the threshold voltage (Vt) of the oxide semiconductor transistor is relatively high (about 1.5 volts for example), and the gate voltage and the drain voltage in operations are also relatively high (about 3.3 volts and 1.2 volts respectively, for example). However, in the condition with the ferroelectric material layer 24 disposed in the oxide semiconductor transistor 100, the gate voltage and the drain voltage for operating the oxide semiconductor transistor 100 may be reduced as the threshold voltage becomes smaller. For example, the gate voltage and the drain voltage may be lower than 1.2 volts, but not limited thereto. In addition, an equation (1) and an equation (2) listed below may be used to calculate the sub-threshold swing of the oxide semiconductor transistor 100.

$\begin{matrix} {{Av} = \frac{C_{FE}}{{C_{FE}} - C_{OX}}} & (1) \end{matrix}$

$\begin{matrix} {{SS} = {60\mspace{14mu}{mV}\text{/}{dec}\frac{1}{Av}}} & (2) \end{matrix}$

In the equation (1) and the equation (2), C_(FE) stands for a capacitance of the ferroelectric material layer 24, C_(ox) stands for a capacitance of the gate insulation layer 22, Av stands for an amplification coefficient, and SS stands for the sub-threshold swing. According to the equation (1) and the equation (2), the capacitance of the ferroelectric material layer 24 has to be larger but the difference between the capacitance of the gate insulation layer 22 and the absolute value of the capacitance of the ferroelectric material layer 24 cannot be too large for avoiding hysteresis effect and resulting in relatively low sub-threshold swing. Additionally, the conventional silicon-based negative capacitance field effect transistor (NCFET) is operated under depletion mode, and the depletion capacitance will influence the amplification coefficient of the negative capacitance and the sub-threshold swing of the transistor. However, the oxide semiconductor transistor in the present invention may be operated under accumulation mode, and the sub-threshold swing may be smaller than that of the silicon-based negative capacitance field effect transistor accordingly.

In this embodiment, the ferroelectric material layer 24 has to be thick enough for generating the required negative capacitance effect, and a thickness of the ferroelectric material layer 24 is larger than a thickness of the gate insulation layer 22, but not limited thereto. The thickness of the gate insulation layer 22 may be reduced (to be less than 20 angstroms for example) for the requirement of low power operations because of the disposition of the ferroelectric material layer 24, but the total thickness of the ferroelectric material layer 24 and the gate insulation layer 22 has to be kept in a substantial range (larger than 100 angstroms for example) for keeping a relatively low off-current (I_(off)) of the oxide semiconductor transistor 100 (about 1E-24 Amp for example). In addition, the oxide semiconductor transistor 100 may further include two source/drain electrodes 30 disposed on the oxide semiconductor channel layer 10 at two opposite sides of the metal gate 29 in a horizontal direction D2. In this embodiment, the source/drain electrodes 30 may be disposed coplanar with the gate insulation layer 22, but the present invention is not limited to this. In some embodiments of the present invention, the allocation of the source/drain electrodes 30 may be further modified, and the source/drain electrodes 30 may be formed in the oxide semiconductor channel layer 10 or be formed at another side of the oxide semiconductor channel layer 10 (such as a side under the oxide semiconductor channel layer 10), for example. In addition, the oxide semiconductor transistor 100 in this embodiment is presented as a planar transistor for demonstration, but the present invention is not limited to this. In other words, other kinds of transistors, such as dual gate transistors, triple gate transistor, or gate all around (GAA) transistors, are within the contemplated scope of the present invention.

A manufacturing method of the oxide semiconductor transistor 100 in this embodiment may include the following steps. The gate insulation layer 22 is formed on the oxide semiconductor channel layer 10. The internal electrode 23 is formed on the gate insulation layer 22. The ferroelectric material layer 24 is formed on the internal electrode 23. The metal gate 29 is formed on the ferroelectric material layer 24. At least a part of the ferroelectric material layer 24 is disposed between the metal gate 29 and the internal electrode 23.

In this embodiment, the oxide semiconductor channel layer 10 may be disposed on a substrate (not shown), and the substrate may include a semiconductor substrate or a non-semiconductor substrate. The semiconductor substrate mentioned above may include a silicon substrate, a silicon germanium substrate, or a silicon-on-insulator (SOI) substrate for example, and the non-semiconductor substrate mentioned above may include a glass substrate, a plastic substrate, or a ceramic substrate for example, but not limited thereto. The materials of the oxide semiconductor channel layer 10 may include II-VI compounds (such as zinc oxide, ZnO), II-VI compounds doped with alkaline-earth metals (such as zinc magnesium oxide, ZnMgO), II-VI compounds doped with IIIA compounds (such as indium gallium zinc oxide, IGZO), II-VI compounds doped with VA compounds (such as stannum stibium oxide, SnSbO₂), II-VI compounds doped with VIA compounds (such as zinc selenium oxide, ZnSeO), II-VI compounds doped with transition metals (such as zinc zirconium oxide, ZnZrO), or other oxide semiconductor materials composed of mixtures of the above-mentioned materials, but not limited thereto. Additionally, the oxide semiconductor channel layer 10 may be a single layer or a multiple layer structure formed by the above-mentioned oxide semiconductor materials, and the crystalline condition of the oxide semiconductor channel layer 10 is also not limited. For example, the oxide semiconductor channel layer 10 may be amorphous IGZO (a-IGZO), crystal IGZO (c-IGZO), or C-axis aligned crystal IGZO (CAAC-IGZO).

The gate insulation layer 22 may include silicon oxide, silicon oxynitride, a high dielectric constant (high-k) material, or other appropriate dielectric materials. The high-k material mentioned above may include hafnium oxide (HfO₂), hafnium silicon oxide (HfSiO₄), hafnium silicon oxynitride (HfSiON), aluminum oxide (Al₂O₃), tantalum oxide (Ta₂O₅), zirconium oxide (ZrO₂), or other appropriate high-k materials. The internal electrode 23 and the metal gate 29 may respectively include conductive metal materials such as tungsten (W), aluminum (Al), copper (Cu), titanium aluminide (TiAl), titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), and titanium aluminum oxide (TiAlO), or other appropriate conductive materials. The ferroelectric material layer 24 may include a perovskite oxide material, such as hafnium zirconium oxide (HfZrO_(x)), barium titanate (BaTiO₃), lead titanate (PbTiO₃), lead zirconate titanate (PbZr_(x)Ti_(1-x)O₃, PZT), and barium strontium titanate (Ba_(x)Sr_(1-x)TiO₃, BST), or other appropriate ferroelectric materials. Additionally, the ferroelectric material layer 24 may be a single layer or a multiple layer structure formed by the above-mentioned ferroelectric materials, and the Curie temperature (T_(c)) of the ferroelectric materials mentioned above is higher than 125 degrees Celsius preferably for presenting the material characteristics under the general operation environment.

The following description will detail the different embodiments of the present invention. To simplify the description, identical components in each of the following embodiments are marked with identical symbols. For making it easier to understand the differences between the embodiments, the following description will detail the dissimilarities among different embodiments and the identical features will not be redundantly described.

Please refer to FIG. 2. FIG. 2 is a schematic drawing illustrating an oxide semiconductor transistor 101 according to a second embodiment of the present invention. As shown in FIG. 2, the difference this embodiment and the first embodiment mentioned above is that the oxide semiconductor transistor 101 in this embodiment further includes a spacer 40 disposed on the oxide semiconductor channel layer 10, and a trench T is formed above the oxide semiconductor channel layer 10. The trench T is surrounded by the spacer 40, and the ferroelectric material layer 24 is disposed in the trench T. In this embodiment, the spacer 40 may include a single layer or a multiple layer structure, such as a first spacer 41 and a second spacer 42 overlapping each other. The first spacer 41 and the second spacer 42 may respectively include silicon oxide, silicon nitride, silicon oxynitride, or other appropriate insulation materials. Additionally, in some embodiments, the metal gate 29 may include a work function layer 29A and a low resistance layer 29B. The work function layer 29A may include titanium nitride (TiN), titanium carbide (TiC), tantalum nitride (TaN), tantalum carbide (TaC), tungsten carbide (WC), titanium tri-aluminide (TiAl₃), or aluminum titanium nitride (TiAlN), but not limited thereto. The low resistance layer 29B may include tungsten, aluminum, titanium aluminide, titanium, or other low resistance materials. In this embodiment, the gate insulation layer 22, the internal electrode 23, and the metal gate 29 are disposed in the trench T. In a cross-sectional view of the oxide semiconductor transistor 101, the gate insulation layer 22 may include a U-shaped structure surrounding the ferroelectric material layer 29 in the trench T, the internal electrode 23 may also include a U-shaped structure surrounding the ferroelectric material layer 24 in the trench T, and the ferroelectric material layer may also include a U-shaped structure surrounding the metal gate 29 in the trench T. Additionally, in the metal gate 29 disposed in the trench T, the work function layer 29A may also include a U-shaped structure surrounding the low resistance layer 29B in a cross-sectional view of the oxide semiconductor transistor 101, but not limited thereto. In addition, the oxide semiconductor transistor 101 may further include an interface layer 21, such as an oxide layer, formed between the gate insulation layer 22 and the oxide semiconductor channel layer 10, but not limited thereto.

Please refer to FIGS. 2-5. FIGS. 3-5 are schematic drawings illustrating a manufacturing method of the oxide semiconductor transistor 101 according to the second embodiment of the present invention. The manufacturing method of the oxide semiconductor transistor 101 in this embodiment may include the following steps. As shown in FIG. 3, the interface layer 21 and a dummy gate 50 are formed on the oxide semiconductor channel layer 10. The dummy gate 50 and the interface layer 21 may be formed by patterning material layers on the oxide semiconductor channel layer 10 simultaneously, such as by etching processes with the same patterned mask, but not limited thereto. As shown in FIG. 4, the spacer 40 is then formed on the oxide semiconductor channel layer 10, and the spacer 40 is formed on sidewalls of the dummy gate 50 and the interface layer 21. In other words, the dummy gate 50 is formed before the step of forming the spacer 40. The first spacer 41 may be formed by a process of forming a conformal material layer on the oxide semiconductor channel layer 10 and the dummy gate 50 and an etching back process. In addition, a planarization process, such as a chemical mechanical polishing (CMP) process, or an etching back process may be used to expose a top surface of the dummy gate 50. Before the planarization process mentioned above, an interlayer dielectric (not shown) may be formed on the spacer 40, and the space between the spacers 40 may be filled with the interlayer dielectric before the planarization process is performed to expose the top surface of the dummy gate 50. As shown in FIG. 4 and FIG. 5, the dummy gate 50 is removed for forming the trench T surrounded by the spacer 40. Subsequently, as shown in FIG. 2, the gate insulation layer 22, the internal electrode 23, the ferroelectric material layer 24, and the metal gate 29 are sequentially formed in the trench T. In other words, the manufacturing method in this embodiment may be regarded as a high-k last replacement metal gate (RMG) process.

Please refer to FIG. 6. FIG. 6 is a schematic drawing illustrating an oxide semiconductor transistor 102 according to a third embodiment of the present invention. As shown in FIG. 6, the difference between this embodiment and the second embodiment mentioned above is that the metal gate 29 in this embodiment is disposed outside the trench T. In other words, when the ferroelectric material layer 24 has to be thick enough, a planarization process may be performed to remove the excess ferroelectric material after the step of filling the trench T with the ferroelectric material layer 24, and the metal gate 29 may then be formed on the ferroelectric material layer 24 and formed outside the trench T.

Please refer to FIG. 7 and FIG. 8. FIG. 7 is a schematic drawing illustrating an oxide semiconductor transistor 103 according to a fourth embodiment of the present invention, and FIG. 8 is a schematic drawing illustrating a manufacturing method of the oxide semiconductor transistor 103 in this embodiment. As shown in FIG. 7 and FIG. 8, the difference between this embodiment and the second embodiment mentioned above is that the gate insulation layer 22 and the dummy gate 50 in this embodiment are formed on the oxide semiconductor channel layer 10 first before the steps of forming the spacer 40 and the trench T. Accordingly, all of the gate insulation layer 22 in this embodiment is disposed under the internal electrode 23 in the vertical direction D1 and the gate insulation layer 22 does not include the U-shaped structure. The manufacturing method in this embodiment may be regarded as a high-k first RMG process. As shown in FIG. 9, in an oxide semiconductor transistor 104 according to a fifth embodiment of the present invention, the metal gate 29 may also be disposed outside the trench T. In other words, when the ferroelectric material layer 24 has to be thick enough, a planarization process may be performed to remove the excess ferroelectric material after the step of filling the trench T with the ferroelectric material layer 24, and the metal gate 29 may then be formed on the ferroelectric material layer 24.

Please refer to FIG. 10 and FIG. 11. FIG. 10 is a schematic drawing illustrating an oxide semiconductor transistor 105 according to a sixth embodiment of the present invention, and FIG. 11 is a schematic drawing illustrating a manufacturing method of the oxide semiconductor transistor 105 in this embodiment. As shown in FIG. 10 and FIG. 11, the difference between this embodiment and the fourth embodiment mentioned above is that the internal electrode 23, the gate insulation layer 22 and the dummy gate 50 in this embodiment are formed on the oxide semiconductor channel layer 10 before the steps of forming the spacer 40 and the trench T. Accordingly, all of the internal electrode 23 in this embodiment is disposed under the ferroelectric material layer 24 in the vertical direction D1 and the internal electrode 23 does not include the U-shaped structure in this embodiment. Additionally, as shown in FIG. 12, in an oxide semiconductor transistor 106 according to a seventh embodiment of the present invention, the metal gate 29 may also be disposed outside the trench T. In other words, when the ferroelectric material layer 24 has to be thick enough, a planarization process may be performed to remove the excess ferroelectric material first, and the metal gate 29 may then be formed on the ferroelectric material layer 24. In this condition, the top surface of the ferroelectric material layer 24 and the top surface of the spacer 40 are substantially coplanar, but not limited thereto. As shown in FIG. 13, in an oxide semiconductor transistor 107 according to an eighth embodiment of the present invention, the metal gate 29 may further cover at least a part of the spacer 40 in the vertical direction D1. For example, the metal gate 29 may cover the first spacer 41 only or cover both the first spacer 41 and the second spacer 42 (not shown in FIG. 13) for ensuring that the capacitance formed by the ferroelectric layer 24 disposed between the metal gate 29 and the internal electrode 23 may meet the requirements.

To summarize the above descriptions, in the oxide semiconductor transistor and the manufacturing method thereof in the present invention, the ferroelectric material layer and the internal electrode are disposed between the metal gate and the gate insulation layer, and the negative capacitance effect is formed because of the material characteristics of the ferroelectric material layer. The purposes of amplifying the gate voltage, increasing the on-current, and lowering the sub-threshold swing may be achieved accordingly. In addition, the gate insulation layer may become thinner without influencing the low leakage current performance because of the ferroelectric material layer disposed in the oxide semiconductor transistor of the present invention, the oxide semiconductor transistor may therefore be used in low power operations, and the application field of the oxide semiconductor transistor may be expanded accordingly.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. An oxide semiconductor transistor, comprising: an oxide semiconductor channel layer; a metal gate disposed on the oxide semiconductor channel layer; a gate insulation layer disposed between the metal gate and the oxide semiconductor channel layer; an internal electrode disposed between the gate insulation layer and the metal gate; a ferroelectric material layer disposed between the internal electrode and the metal gate; and a spacer disposed on the oxide semiconductor channel layer, wherein a trench surrounded by the spacer is formed above the oxide semiconductor channel layer, the ferroelectric material layer is disposed in the trench, and the metal gate is disposed outside the trench.
 2. The oxide semiconductor transistor of claim 1, wherein a thickness of the ferroelectric material layer is larger than a thickness of the gate insulation layer.
 3. The oxide semiconductor transistor of claim 1, wherein the ferroelectric material layer comprises a perovskite oxide material.
 4. The oxide semiconductor transistor of claim 1, wherein the oxide semiconductor channel layer includes indium gallium zinc oxide (IGZO).
 5. The oxide semiconductor transistor of claim 1, wherein the gate insulation layer is disposed in the trench, and the gate insulation layer comprises a U-shaped structure surrounding the ferroelectric material layer in the trench.
 6. The oxide semiconductor transistor of claim 1, wherein the internal electrode is disposed in the trench, and the internal electrode comprises a U-shaped structure surrounding the ferroelectric material layer in the trench.
 7. A manufacturing method of an oxide semiconductor transistor, comprising: forming a gate insulation layer on an oxide semiconductor channel layer; forming an internal electrode on the gate insulation layer; forming a ferroelectric material layer on the internal electrode; forming a metal gate on the ferroelectric material layer, wherein at least a part of the ferroelectric material layer is disposed between the metal gate and the internal electrode; and forming a spacer on the oxide semiconductor channel layer before the step of forming the ferroelectric material layer, wherein a trench surrounded by the spacer is formed above the oxide semiconductor channel layer, and the metal gate is formed outside the trench.
 8. The manufacturing method of the oxide semiconductor transistor of claim 7, wherein the step of forming the trench comprises: forming a dummy gate on the oxide semiconductor channel layer before the step of forming the spacer, wherein the spacer is formed on a side wall of the dummy gate; and removing the dummy gate for forming the trench surrounded by the spacer.
 9. The manufacturing method of the oxide semiconductor transistor of claim 7, wherein the ferroelectric material layer is formed after the step of forming the trench, and the ferroelectric material layer is formed in the trench.
 10. The manufacturing method of the oxide semiconductor transistor of claim 9, wherein the internal electrode is formed after the step of forming the trench, and the internal electrode is formed in the trench.
 11. The manufacturing method of the oxide semiconductor transistor of claim 10, wherein the internal electrode comprises a U-shaped structure surrounding the ferroelectric material layer in the trench.
 12. The manufacturing method of the oxide semiconductor transistor of claim 10, wherein the gate insulation layer is formed after the step of forming the trench, and the gate insulation layer is formed in the trench.
 13. The manufacturing method of the oxide semiconductor transistor of claim 12, wherein the gate insulation layer comprises a U-shaped structure surrounding the internal electrode in the trench. 